Fig. 1. Experimental device

Fig. 2. Experimental result
(a): TEM image of silver sol; (b): Size distribution of silver nanoparticles

Fig. 3. Experimental result
(a): The length of fiber microcavity varies with etching time; (b): Raman spectrum of R6G;(c): The composite Raman strength varies with etching time of fiber at 1 362 cm^-1

Fig. 4. Experimental process of the sol self-assembly method of optical fiber SERS probe

Fig. 5. SEM image of Ag/fiber-30 substrate at different areas
(a)—(f): 10~60 minutes in area a; (g)—(l): 10~60 minutes in area b

Fig. 6. Experimental results
(a): Raman spectra of 10^-3 mol·L^-1 R6G detected using fiber SERS substrates with different self-assembly times;(b): Enlarged figure of Raman intensity at 1 510 cm^-1

Fig. 7. Sensitivity test on different substrates
(a): Nano-silver sol substrate; (b): Ag/Fiber-30 substrate

Fig. 8. Relationship between Raman intensity and R6G concentration
(a): Nano-silver sol substrate;(b) Ag/Fiber-30 substrate (all the error bars were calculated based on five independent measurements)

Fig. 9. Reproducibility test results and RSD values of different substrates
(a): Nano-silver sol; (b): Ag/Fiber-30

Fig. 10. Experimental results
(a): Stability test of nano silver sol substrate; (b): Stability test of Ag/Fiber-30 substrate; (c)—(e): Raman spectra of R6G